There is an ongoing demand in the aerospace industry for low cost electromagnetic coils suitable for usage in coiled-wire devices, such as actuators (e.g., solenoids and motors) and sensors (e.g., rotary and linear variable differential transformers), capable of providing prolonged and reliable operation in high temperature environments and, specifically, while subjected to temperatures in excess of 260° C. It is known that low cost electromagnetic coils can be produced utilizing aluminum wire, which is commercially available at minimal cost, which provides suitable conductive properties, and which can be anodized to form an insulative alumina shell over the wire's outer surface. Aluminum wire is, however, highly susceptible to working hardening and mechanical fatigue during physical manipulation, especially if the aluminum wire is of a relatively fine gauge; e.g., 30-36 American Wire Gauge. Work hardening of the aluminum wire may result in breakage of the wire during assembly and/or termination, including termination to wires of differing diameters and material types. Work hardening may accelerate open circuit failure during subsequent device operation. Thus, to reduce the application of stress to a relatively fine gauge aluminum wire during manufacture of an electromagnetic coil assembly, it may be desirable to splice each end of the aluminum wire to a different wire less susceptible to work hardening and breakage.
Crimping has long been utilized to electrically and mechanically join wires together. Crimping of the fine gauge aluminum wire can, however, result in work hardening of the aluminum wire of the type described above. In addition, for instances wherein the aluminum wire is crimped to a second wire fabricated from a metal having a hardness exceeding that of aluminum, the deformation induced by crimping may be largely concentrated in the aluminum wire and an optimal physical mechanical and/or electrical bond may not be achieved. In contrast to crimping, soldering does not require the application of deformation forces to the wire-to-wire interface, which can cause the above-noted issues with fine gauge aluminum wire. However, soldering of fine gauge aluminum wire also presents certain difficulties. Due to its relatively low melt point and thermal mass, fine gauge aluminum wire can easily be overheated and destroyed during the solder processing. The likelihood of inadvertently overheating the aluminum wire is especially pronounced when soldering is carried-out in a relatively confined space utilizing, for example, a microtorch. Heating during soldering can also result in formation of oxides along the wires' outer surfaces increasing electrical resistance across the solder joint. As a still further drawback, moisture present at the solder interface can accelerate corrosion and eventual connection failure when aluminum wire is joined to a secondary wire formed from a metal, such as copper, having an electronegative potential that differs significantly as compared to aluminum wire.
It would thus be desirable to provide methods and means for reliably soldering aluminum wire, especially fine gauge aluminum wire, to a secondary wire that avoids the above-noted limitations associated with conventional soldering processes. Ideally, such a soldering method and means would facilitate the formation of a wire-to-wire solder connection having a relatively low ohmic resistance and a relatively high corrosion resistance. It would also be desirable for such an aluminum wire soldering method and means to be usefully applied in the production of electromagnetic coil assemblies, such as high temperature electromagnetic coil assemblies included within coiled-wire devices (e.g., actuators and sensors) deployed onboard aircraft. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.